CN110445406A - A kind of bimodal smooth transition control method of PWM rectifier - Google Patents

Abstract

The invention discloses a dual-mode smooth transition control method of a PWM rectifier. The method is that a modulation ratio soft-start controller is added between the double-closed-loop controller of the PWM rectifier and the PWM pulse signal generation module. The start-up controller makes the modulation ratio of the PWM rectifier gradually decrease from large to small to the steady-state value, thereby suppressing the start-up inrush current of the PWM rectifier. The structure of the modulation ratio soft-start controller is divided into three parts. , the mathematical model of the modulation ratio soft-start controller is k = 0; between the start time t ₀ and the start-up end time t ₁ , the mathematical model of the modulation ratio soft-start controller is k = k ₂ ‑ k ₁ t , the modulation ratio After the soft start, the mathematical model of the modulation ratio soft start controller becomes k = 1; the modulation ratio soft start controller is started in sections to completely eliminate the inrush current generated at the start time of the PWM rectifier and achieve the purpose of smooth transition.

Description

A dual-mode smooth transition control method for PWM rectifiers

technical field

The invention relates to a control method for a three-phase voltage PWM rectifier, in particular to a safety control method for the PWM rectifier without current impact.

Background technique

Because the PWM rectifier mainly controls the charging and discharging time of the AC side filter inductor to supply power to the DC side through the on-off of the bridge arm IGBT when it starts up, so the three-phase PWM rectifier can be divided into two types from the state of the filter inductor, one is the inductor Charging, saving energy; the other is that the inductor discharges to charge the DC side, and when the charging time and discharging time reach a balance, the DC side voltage will be stable; when the PWM rectifier starts, if the initial modulation ratio amplitude is small, it will lead to the first One kind of circuit state time is too long. At this time, the inductance is approximately connected between the two-phase power supply on the AC side, and the current growth rate is fast, causing a large inrush current to affect the life and safety of the system.

Commonly used starting surge current suppression methods are: clipping method, such as publication number: CN104734481A; target voltage value parabolic law start method, such as publication number: CN103904873A; vector soft start method, such as publication number: CN107196496A, and parabolic Superimposed ramp function startup method, such as the publication number: CN105915039A, according to the formula , the common point of these methods is to reduce the output value of the voltage outer loop PI regulator, that is, the reference value id ^* of the _d axis of the current inner loop _. When the actual current increases greater than the reference value id ^* , m _d will increase , so as to reduce the charging time of the grid-side inductance and reduce the inrush current, but the common point of these methods is that the actual system current is greater than the rated current, that is, the inrush current will be generated, and the suppression effect will not be suppressed. In the beginning, the inrush current was caused by too small modulation ratio.

Contents of the invention

In order to improve the deficiencies of the above-mentioned existing control methods, the present invention provides a dual-mode smooth transition control method for a PWM rectifier. Controller, modulation ratio The function of the soft-start controller is to suppress the inrush current by changing the modulation ratio and then changing the switching mode when the inrush current of the PWM rectifier has not yet been generated. The specific technical scheme is as follows:

A dual-mode smooth transition control method for a PWM rectifier, characterized in that: the dual-mode smooth transition control method is to add a modulation ratio soft-start control between the dual closed-loop controller of the PWM rectifier and the PWM pulse signal generation module device; the double closed-loop controller is used to control the voltage stability of the DC side of the PWM rectifier; the modulation ratio soft-start controller is used to amplify the modulation ratio when the PWM rectifier is started, and suppress the start-up inrush current; the PWM pulse generation module It is used to generate the PWM pulse signal to control the switch to conduct.

In the above technical solution: the PWM rectifier is first calculated by the double closed-loop controller to obtain the three-phase modulation ratio ma , m _{b ,} m _c ; then input ma, m b _{, m} c _into the modulation ratio The soft-start controller calculates new three-phase modulation _ratios ma ^* _{, mb} ^* , and mc _* , and then outputs switching signals from the PWM pulse signal generating module to control the PWM rectifier to start working.

A further technical solution is: the design process when the PWM rectifier double closed-loop controller and the modulation ratio soft-start controller are started is:

(1) Establish the controller mathematical model of the rectifier in the dq coordinate system as:

Among them: K _vP , K _vI , K _iP , K _iI are the proportional coefficients and integral coefficients of the voltage outer loop and the current inner loop respectively; v _dc ^* is the reference value of the DC bus voltage; i _d ^* , i _d ^* are the current The given values of the d-axis and q-axis of the ring, i _d , i _q are the components of the actual grid-side current on the d-axis and q-axis respectively, ω is the fundamental angular frequency of the grid-side voltage, i _cd , i _cq are respectively the filter capacitor current at The components of d-axis and q-axis, L _T is the AC side inductance ( L _T = L ₁ + L ₂ );

(2) Calculate the three-phase modulation ratio according to the d-axis and q-axis components of the modulation ratio obtained in (1), and the calculation formula is:

Where: m _a , m _b , m _c are the three-phase modulation ratios, C _{2 r /3 s} is the transformation matrix from the three-phase stationary coordinate system to the two-phase rotating coordinate system;

(3) Input the three-phase modulation ratio in (2) into the modulation ratio soft-start controller, and the expression of the new modulation ratio is obtained as:

Among them: m _a ^* , m _b ^* , m _c ^* are the modulation ratio output by the soft start controller;

(4 ₎ Control the conduction of the PWM rectifier according to the three-phase _modulation ratios ma ^* _, mb ^* , _mc * output by the modulation ratio soft-start controller.

A further technical solution is that the mathematical model k of the modulation ratio soft-start controller at start-up is as follows:

In the function k expression:

v _trm is the triangular carrier amplitude, T _s is the triangular carrier period, ω is the fundamental angular frequency of the grid side voltage, t ₁ is the soft start and end time of the modulation ratio, t ₀ is the start time of the PWM _rectifier , ed is the three-phase modulation ratio The d-axis transformation component of , v _dc is the DC side voltage.

Among them: when the PWM rectifier starts, the modulation ratio soft-start controller is an inverted slope function whose linear law decreases to 1.

The dual-mode smooth transition control method of the PWM rectifier provided above in the present invention, compared with the existing voltage soft-start technology, adds a modulation ratio soft-start controller, and can controllably start the PWM rectifier by amplifying the modulation ratio. Gradually increase the charging time of the inductor to suppress the generation of inrush current.

Description of drawings

Fig. 1 is the main circuit and control diagram of the PWM rectifier of the present invention.

Fig. 2 is a mathematical model curve diagram of the modulation ratio soft-start controller of the present invention.

Fig. 3 is the experimental waveform of the direct start PWM rectifier of the present invention.

Fig. 4 is the soft-start experiment waveform of the PWM rectifier voltage reference ramp in the present invention.

Fig. 5 is a soft-start experiment waveform based on the modulation ratio of the PWM rectifier of the present invention.

Detailed ways

The specific implementation manners of the present invention will be further described below.

Implement a dual-mode smooth transition control method for a PWM rectifier, the dual-mode smooth transition control

The preparation method is carried out according to the following steps:

Step 1: When the PWM rectifier is started, the three-phase modulation ratios ma , m _{b ,} m _c are calculated by the double closed-loop controller;

Step 2: within the starting time t ₀ - t ₁ , the soft-start controller calculates the input modulation ratios of ma, m b, m c _{to obtain} new _{three -} phase modulation ratios ma ^* , m _b ^* _, m _c *;

Step ₃ : According to the new three-phase modulation _ratios ma ^* _{, mb} ^* , mc ^* , the PWM pulse signal generating module outputs pulse signals to control the work of the PWM rectifier.

The specific content of the first step includes: firstly, the diode on the three-phase bridge arm performs uncontrolled rectification, completes the pre-charging process of the DC side capacitor, and then detects whether the AC voltage amplitude, frequency, AC side current and DC side voltage are within the normal range After the detection is completed, the grid-side voltage and current signals are collected and the AC components are converted into DC components in the dq coordinate system, and the voltage and current double closed-loop, grid voltage feed-forward calculation and current inner loop decoupling calculation are completed to obtain the modulation ratio d-axis, The q-axis component, the three-phase modulation ratios ma , m _{b ,} m _c are obtained through coordinate transformation.

The specific content of the second step includes: input the three-phase modulation ratios ma , m _{b ,} m _c obtained in the first step into the modulation ratio soft-start controller to obtain a new three-phase modulation ratio , the expression of the proportional coefficient k :

In the function k expression:

The calculation formula of m0 is _:

v _trm is the triangular carrier amplitude, T _s is the triangular carrier cycle, ω is the grid-side voltage fundamental angular frequency, t ₁ is the soft start and end time of the modulation ratio, t ₀ is the starting time of the PWM _rectifier , ed is the grid-side three-phase The d-axis transformation component of the voltage, v _dc is the DC side voltage.

The specific content of the third step includes: using the SPWM principle, the three-phase modulation ratio obtained in the second step is used to generate a switching signal of the three-phase bridge arm to control the operation of the PWM rectifier.

Specific embodiment 1

Specific embodiments of the present invention are described in conjunction with accompanying drawings 1 and 2, accompanying drawing 1 is a PWM rectifier main circuit and control diagram, v _dc is a direct current voltage, S _ap , S _an , S _bp , S _bn , S _cp , S _cn is the six IGBT switch tubes of the three-phase rectifier, e _a , e _b , e _c are the grid voltage, L ₁ , L ₂ , and C ₁ are the grid-side inductance, inverter-side inductance and filter capacitor of the LCL filter , R ₁ R ₂ inductor parasitic resistance, i _dc is the input current of DC power supply, i _ga , i _gb , i _gc are grid side currents, i _La , i _Lb , i _Lc are bridge arm side currents, C is DC side capacitance, R is the load on the DC side; the specific embodiment of the present invention describes a dual-mode smooth transition control method for a PWM rectifier. When the PWM rectifier is started, it mainly controls the amplitude of the three-phase modulation ratio, and then gradually increases the filter inductance of the AC side. The charging time is long enough to achieve the purpose of starting the three-phase PWM rectifier without inrush current. The specific steps are as follows:

Step 1: Firstly, the diode on the three-phase bridge arm performs uncontrolled rectification to complete the pre-charging of the DC side capacitor.

Step 2: Detect whether the AC voltage amplitude, frequency, AC side current and DC side voltage are within the normal value range. After the detection is completed, collect the network side voltage, filter capacitor current, and current signal and convert the AC component into the dq coordinate system the DC component.

Step 3: Slowly increase the given value v _dc ^* of the DC side voltage according to the function curve 1 shown in attached drawing 1, and calculate the d-axis and q-axis components m _d and m _q of the three-phase modulation ratio according to the following formula;

.

Step 4: According to The three-phase modulation ratios ma , m _{b ,} m _c are obtained.

Step 5: Let the three-phase modulation ratios ma , m _{b ,} m _c obtained in step ₄ be input to the modulation ratio soft-start controller to obtain new three-phase modulation ratios ma ^* , m _b ^* _, m _c * to control the PWM rectifier conduction work.

The above-mentioned mathematical model of the modulation ratio soft-start controller at the start time is a piecewise function composed of an inverted ramp function and a constant function. The function expression of the mathematical model k is as follows:

In the function k expression:

The calculation formula of m0 is _:

In the formula: vtrm is the triangular carrier amplitude, T _s is the period _of the triangular carrier, ω is the fundamental angular frequency of the grid side voltage, _t1 is the end time of the soft start of the modulation ratio, _t0 is the starting time of the PWM rectifier, and e _d is the grid side voltage The d-axis transformation component of the side three-phase voltage, v _dc is the DC side voltage.

Step 6: Using the principle of SPWM, calculate the three-phase modulation ratio obtained in the fifth step to obtain the switching signal of the three-phase bridge arm to control the operation of the PWM rectifier.

The above specific embodiments amplify the modulation ratio when the PWM rectifier starts, thereby avoiding the surge current generated when the PWM rectifier transitions from an uncontrollable state to a controllable state.

Claims (5)

1. a kind of bimodal of PWM rectifier seamlessly transits control method, it is characterised in that: the bimodal smooth transition control Method is to have additional that modulation ratio is soft to open control between the double-closed-loop control device and pwm pulse signal generation module of PWM rectifier Device；The double-closed-loop control device is for controlling PWM rectifier DC-side Voltage Stabilization；The soft controller that opens of the modulation ratio is to use To amplify modulation ratio when PWM rectifier starting, inhibition inrush current；The pwm pulse generation module is for generating The control switch device of pwm pulse signal is connected.

2. the bimodal of PWM rectifier as described in claim 1 seamlessly transits control method, it is characterised in that: the PWM is whole Stream device is that three-phase modulations ratio first is calculated by double-closed-loop control device on startupm _a 、m _b、 m _c ；Then willm _a 、m _b、 m _c Described in input New three-phase modulations ratio is calculated in the soft controller that opens of modulation ratiom _a ^*、m _b ^* _、 m _c *, then it is defeated by the pwm pulse signal generation module Switching signal out controls the PWM rectifier and starts to work.

3. the bimodal of PWM rectifier as claimed in claim 2 seamlessly transits control method, it is characterised in that: the PWM is whole Stream device double-closed-loop control device and the soft design process opened when controller starts of modulation ratio are as follows:

(1) controller mathematical model of the rectifier under dq coordinate system is established are as follows:

Wherein:K _vP ,K _vI ,K _iP ,K _iI It is the proportionality coefficient and integral coefficient of outer voltage, current inner loop respectively；v _dc ^*It is direct current mother The reference value of line voltage；i _d ^*,i _d ^*It is the given value of electric current loop d axis and q axis respectively,i _d ,i _q Respectively practical current on line side d axis with The component of q axis,ωFor voltage on line side fundamental wave frequency,i _cd ,i _cq Respectively filter capacitor electric current d axis and q axis component,L _T To hand over Stream side inductance (L _T =L ₁+L ₂)；

(2) three-phase modulations ratio, calculation formula is calculated in modulation ratio d axis, q axis component according to obtained in (1) are as follows:

Wherein:m _a,m _b,m _cFor three-phase modulations ratio,C _2r/3s For the transformation matrix of three-phase static coordinate system to two-phase rotating coordinate system；

(3) by the three-phase modulations in (2), than input, modulation ratio is soft opens controller, obtains new modulation ratio expression formula are as follows:

Wherein:m _a ^*、m _b ^*、m _c ^*For the soft modulation ratio for opening controller output of modulation ratio；

(4) according to the soft three-phase modulations ratio for opening controller output of modulation ratiom _a ^*、m _b ^* _、 m _c * PWM rectifier ON operation is controlled.

4. the bimodal of PWM rectifier as claimed in claim 3 seamlessly transits control method, it is characterised in that: tune when starting System is than the soft mathematical model for opening controllerkIt is as follows:

FunctionkIn expression formula:

v _trmFor triangular carrier amplitude, T_sFor the triangular carrier cycle,ωFor voltage on line side fundamental wave frequency,t ₁It is tied for modulation ratio soft The beam moment,t ₀For PWM rectifier Startup time,e _d For the d principal axis transformation component of three-phase modulations ratio,v _dc For DC voltage.

5. the bimodal of PWM rectifier as claimed in claim 4 seamlessly transits control method, it is characterised in that: PWM rectifier The soft controller that opens of modulation ratio is the ramp function that falls that a linear rule is decremented to 1 when starting.